Nutritional biologist Quinn Carter explains why intermittent fasting (IF) has become one of the most widely studied approaches for fat reduction in recent years. Intermittent fasting is not simply about eating fewer calories. The practice can influence the way the body uses stored energy and may cause important metabolic changes that support fat burning. By extending the time between meals, the body gradually shifts away from relying mainly on recently consumed food and begins using stored energy. According to Quinn, this metabolic response is one of the main reasons intermittent fasting continues to attract attention in nutrition and weight-management research.
How Fasting Changes the Body’s Energy Source
After several hours without food, the body starts using its stored energy reserves. Quinn explains that during longer fasting periods, commonly around 12 to 16 hours, the body may begin increasing its reliance on stored fat and producing ketones. This metabolic state is commonly associated with ketosis, although the exact timing and level of ketone production can vary significantly from person to person.
As insulin levels generally decline during fasting, stored fat can become more accessible as an energy source. This process may help improve metabolic flexibility, which refers to the body’s ability to switch between carbohydrates and fats for fuel. Quinn also highlights the relationship between fasting and insulin sensitivity. Better insulin sensitivity can support healthier blood sugar regulation and may play an important role in long-term metabolic health and weight management.
Intermittent Fasting and Autophagy
Another interesting area of fasting research is autophagy, a natural cellular recycling process. During autophagy, cells break down and reuse damaged or unnecessary cellular components. Quinn describes it as the body’s internal cellular clean-up system, although it should not be confused with a literal “detox” process.
Research suggests that fasting and nutrient restriction can influence pathways connected with autophagy. However, exactly when autophagy significantly increases in humans is still being investigated, and there is no universal fasting duration that guarantees its peak. Longer fasting periods, including fasting beyond 18 hours, are often discussed in this context, but responses can differ depending on metabolism, activity levels, diet and overall health.
Some people following intermittent fasting report improved energy, concentration and mental clarity. These experiences may be connected with several factors, including changes in eating patterns, blood sugar regulation and the body’s increased use of fat and ketones for energy. Individual experiences, however, can vary considerably.
Starting With a 14:10 Fasting Schedule
For people who are new to intermittent fasting, Quinn recommends beginning gradually rather than immediately attempting a long fasting period. A 14:10 schedule can be a practical starting point. Under this approach, a person fasts for 14 hours and consumes meals within a 10-hour eating window.
Once the body becomes comfortable with this routine, some people may choose to move toward a 16:8 schedule. This involves fasting for 16 hours and eating during an eight-hour window. The approach can make meal timing more structured while still providing enough time to consume balanced meals.
Fasting Does Not Mean Deprivation
Quinn emphasizes that successful intermittent fasting should not be treated as starvation or extreme food restriction. The quality of food consumed during the eating window remains extremely important. Simply fasting for several hours and then relying on highly processed or nutrient-poor foods may make it harder to meet nutritional needs.
Nutrient-dense meals containing adequate protein, vegetables, fruits, whole grains, healthy fats and other minimally processed foods can help provide essential vitamins and minerals. Protein is particularly important for supporting muscle maintenance, especially when intermittent fasting is being used alongside a calorie deficit for fat reduction.
Why Women May Need a Different Fasting Approach
Quinn points out that women may benefit from a more flexible approach to intermittent fasting because energy availability, hormonal changes and individual health needs can affect the way fasting is tolerated. Instead of beginning with long fasting periods, some women may prefer starting with a shorter fasting window of approximately 12 to 14 hours.
She also discusses circadian rhythm fasting, an approach that attempts to align food intake more closely with the body’s natural daily biological clock. This often means consuming most meals during daylight hours and avoiding very late-night eating. Research into meal timing suggests that eating earlier in the day may offer metabolic advantages for some people, although individual schedules and health requirements should also be considered.
Intermittent Fasting Is Not Suitable for Everyone
Although intermittent fasting can be a useful strategy for some people, Quinn stresses that it is not appropriate for everyone. Individual health conditions, medications, nutritional requirements and previous eating behaviors should be considered before making a major change to meal timing.
People with certain medical conditions, those who are pregnant or breastfeeding, individuals taking medications affected by food intake, and people with a current or previous history of disordered eating may require special guidance or may need to avoid fasting altogether.
Intermittent fasting should therefore be viewed as one possible nutrition strategy rather than a guaranteed solution for fat loss. Results depend on overall calorie intake, food quality, physical activity, sleep, stress, genetics and individual metabolic health. Anyone considering a major change in fasting duration or eating habits should consult a qualified healthcare professional or registered dietitian, particularly if they have an existing health condition or take regular medication.